1. Field of the Invention
The invention relates to an internal combustion engine, to a method for operating an internal combustion engine and to a control device for carrying out the method.
2. Description of the Related Art
Internal combustion engines with multi-stage exhaust gas supercharging are thoroughly known from practice. Accordingly, an internal combustion engine with multi-stage exhaust gas supercharging comprises multiple cylinders and multiple exhaust gas turbochargers, wherein in the turbines of the exhaust gas turbochargers exhaust gas leaving the internal combustion engine is expanded, and wherein energy extracted in the turbines of the exhaust gas turbochargers is utilized in the compressors of the exhaust gas turbochargers in order to compress charge air to be fed to the cylinders of the internal combustion engine. In the case of an internal combustion engine with a high-pressure exhaust gas turbocharger and a low-pressure exhaust gas turbocharger, the exhaust gas leaving the internal combustion engine is initially expanded in the high-pressure turbine of the high-pressure exhaust gas turbocharger and subsequently for further expansion conducted via the low-pressure turbine of the low-pressure exhaust gas turbocharger. Energy extracted in the low-pressure turbine of the low-pressure turbocharger is utilized in order to compress charge air to be fed to the cylinders of the internal combustion engine initially in the low-pressure of the low-pressure exhaust gas turbocharger, wherein already compressed charge air leaving the low-pressure compressor is further compressed in the high-pressure compressor of the high-pressure exhaust gas turbocharger, namely utilizing the energy in the high-pressure turbine of the high-pressure exhaust gas turbocharger. In this case, a so-called charge air cooler each can be positioned downstream of the low-pressure compressor and upstream of the high-pressure compressor, a so-called charge air cooler each can be positioned in this case.
From practice it is already known, furthermore, to position a selective catalytic reduction (SCR) catalytic converter in supercharged internal combustion engines between the high-pressure turbine of the high-pressure exhaust gas turbocharger and the low-pressure turbine of the low-pressure exhaust gas turbocharger, so that exhaust gas expanded in the high-pressure turbine of the high-pressure exhaust gas turbocharger is initially conducted via the SCR catalytic converter and only following this via the low-pressure turbine of the low-pressure exhaust gas turbocharger. The temperatures and pressures that are present downstream of the high-pressure turbine and upstream of the low-pressure turbine are particularly advantageous for the exhaust gas aftertreatment in an SCR catalytic converter.
Such an SCR catalytic converter has a relatively high heat capacity, so that in particular after the start of the internal combustion engine or during load jumps of the same relatively much thermal energy of the exhaust gas for heating-up the SCR catalytic converter is lost, so that accordingly a greater exhaust gas temperature gradient can form via the SCR catalytic converter. This can result in the low-pressure turbine of the low-pressure exhaust gas turbocharger no longer being able to provide an adequate amount of energy required in the low-pressure compressor of the low-pressure exhaust gas turbocharger to ultimately supply the cylinders of the internal combustion engine with a desired charge air quantity. Because of this, the so-called load impact capability of the internal combustion engine is restricted in particular during the cold start of an internal combustion engine or during load jumps.